With nerd power and geek chic abounding at San Diego Comic-Con 2013, it's no wonder that the panel for TV's most popular comedy, "The Big Bang Theory," is a major draw for fans. But this year, the panel was missing some of the "zing" in "bazinga" without any cast members onstage. (Of course, the show would be nothing without the creative team, but still!)

Luckily, the star power came in a superpowered way: Johnny Galecki, who plays Dr. Leonard Hofstadter, crashed the panel in costume! And not just any costume: The "Big Bang" star, posing as an eager fan, stood up to ask a question dressed up in "Star Wars" duds — more specifically, the masked Ubese bounty hunter Boushh from "Return of the Jedi." The panel members insisted that he remove his mask, and (bazinga!) it was the one and only Galecki. Even more awesome, Galecki hopped onstage and joined the panel for the rest of the discussion.

"Big Bang Theory" fans know that the comedy's speedy theme song is tricky to memorize, and according to a surprise guest, physicist and author Stephen Hawking, you only really need the first two lines — which Hawking sung via a prerecorded video segment — to sum up the existence of, well, everything. Thanks, Stephen!

Watch Hawking's guest appearance:

2. Another Star From the "Big Bang" Galaxy

Melissa Rauch, who plays sassy microbiologist Bernadette Rostenkowski-Wolowitz (wife of Howard Wolowitz, played by Simon Helberg), shocked attendees by showing up as the panel's guest moderator. Way to go, Bernie!

In the event's most touching moment, the first question asked of the panel was from a young fan who had been granted a wish from the Make A Wish foundation. That's proof enough of how CBS's comedy juggernaut has affected devotees of all ages and backgrounds.

Sheldon Cooper (played by two-time Emmy Award winner Jim Parsons) is so logical, he's downright illogical at times, which might be why he's never gotten intimate with girlfriend Amy Farrah Fowler (Mayim Bialik). But that might change in Season 7! Sure, there was an oh-so-awkwardly memorable spanking in Season 6, but that's not the same thing. According to executive producer Steven Molaro, "it's a possibility" that these two geniuses are going to get physical soon. By the way, that infamous spanking scene was inspired by a real-life experience from writer Maria Ferrari's high school days.

Season 6 ended with a surprise revelation, and he just couldn't shut up! Raj Koothrappali (played by Kunal Nayyar) has always needed liquid courage to say even one word in front of any lady, but after getting his heart shattered by ex-girlfriend Lucy (Kate Micucci), he was venting ad nauseam sans alcohol. By the final scene in Season 6, the "Big Bang" ladies couldn't get the astrophysicist to zip it. According to the panel, Raj will be different and much more vocal in Season 7!